The invention relates to a method and arrangements for measuring the condition of a base station in a TDMA radio system, in which are used TDMA channel structures according to ETSI/GSM recommendation 05.02, by means of test measurements performed in predetermined TDMA time slots.
One of the most critical factors in radio systems, for instance in cellular radio telephone systems, is the quality of a radio link between a base station and a mobile radio station. The quality of this radio link is essentially affected by the condition of radio sections of the base station, i.e. antennas and transceivers. Therefore, it is important to be able to monitor the condition of the radio sections of the base station by various measurements and tests.
The condition of the transmitting and receiving antennas of a base station is typically monitored by measuring the standing wave ratio thereof, i.e. electrical matching of the antennas to the remaining part of the receiver and transmitter system. This has normally been performed by means of an equipment positioned at the base station, supplying RF power through an antenna line to the antenna and measuring the power reflected from the antenna. The condition of the antenna has been concluded from the level of the signal reflected from the antenna. The measurements are usually carried out at a specific test frequency outside the normal operating frequency band of the base station, in order to avoid disturbance to the normal operation of the base station. Some equipments applying this principle are described in the Finnish Patent Application 904085 as well as in the European Patent Application 0 261 828.
The condition of transceivers as well as baseband signal processing units of a base station have been tested by an equipment looping an RF test signal sent by a transmitter to a receiver. If the sent test signal is received error free, the devices to be tested are assumed to be in a proper condition. In digital radio systems, it is possible to calculate on the basis of a comparison between transmitted and received data a Bit Error Rate (BER), which is below a predetermined limit value at a base station in a proper condition. The radio test equipment is typically connected between transmitting antenna line and receiving antenna line and it has to convert the test signal from transmission frequency to reception frequency. Some equipments of this type are described in the Finnish Patent Application 902624 and in the PCT Application WO90/06635.
New digital radio systems of the TDMA (Time Division Multiple Access) type have time-division signalling including several, typically 8, time slots at one frequency. One TDMA system is the Pan-European mobile telephone system GSM (Groupe System Mobile). Also in the digital radio systems, the test measurements have to be carried out at frequencies outside the normal frequency band of the base station, if it is not desirable to disturb the normal operation of the base station. If normal frequencies of the base station are desired to be used for the test measurements performed during the operation of the base station, it is necessary to remove one of the time slots from the "normal traffic" for test use. For this reason, a continuous monitoring of the radio sections of the base station and real-time alarms have not been possible.